Production Part Approval Process (PPAP) - A Guide
01. What is a Production Part Approval Process (PPAP)?
A PPAP (Production Part Approval Process) is a new-product introduction business process that determines whether a manufacturer is capable of consistently delivering parts that conform to specifications.
A PPAP is important for both the buyer and the supplier (manufacturer) of a part.
For the supplier, a PPAP is an opportunity to evaluate the manufacturability of a part, ensure completeness of the design documentation, identify design errors, recommend design changes to improve manufacturability, and establish the manufacturing process and supply chain for the part.
For the buyer, the PPAP is an opportunity to confirm that the design requirements have been understood, and that the supplier's manufacturing process, external special processing steps, and functional testing are indeed capable of consistently delivering good parts.
The PPAP process involves a comprehensive review of the engineering documentation (drawings, spec sheets) and the manufacturing process from raw materials through conversion (machining, molding, casting etc.), special processing (anodization, plating, hardening etc.) and all the way through functional testing for an initial set of parts.
02. When is a PPAP needed?
A PPAP is required first during the new product introduction process and subsequently a delta PPAP is required for any change to the design or manufacturing process.
Once a PPAP is approved, we assume that every subsequent part is built to the same set of design requirements, and is built with the same manufacturing process as defined in the PPAP. Any change in the part's design or in the manufacturing process violates this assumption, and therefore requires a new PPAP.
Here's a partial list of conditions or events that will trigger a new PPAP:
- New Product Introduction
- Design Change (new Part Number or Revision)<.li>
- Manufacturing Process Change
- Vendor Change
- Factory Move
- Resuming Production After a Long Gap
Some of these changes require a complete new PPAP. For example, a change in manufacturing process from 4-axis CNC to a swiss screw lathe, will require a complete new PPAP. A more localized change, to a powder coating process for example, or a change to the packaging of part, may not require a full PPAP. Instead, a delta PPAP may be sufficient.
03. PPAP Levels
The PPAP Levels define the set of documents required for a given part. There are five commonly used levels, but it is common for each company to customize these levels to address their own industry-specific requirements.
Commonly used levels:
Level 1: Core PPAP documents are created. But only the Part Submission Warrant (PSW) is submitted to the customer. ALl other documents are retained and made available to the customer upon request.
Level 2: Core PPAP documents are created. But only the Part Submission Warrant (PSW), product samples and a subset of documents are submitted to the customer. Other documents are retained and made available to the customer upon request.
Level 3: CorePPAP documents are created and submitted to the customer along with product samples.
Level 4: Core PPAP documents are created and submitted to the customer along with product samples and any additional customer requested documents.
Level 5: Core PPAP documents are created. Product samples and complete supporting data is retained by the supplier and made available to the customer for review upon request.
04. Commonly Requested PPAP Elements
There are a number of industry-standard PPAP requirements:
- Design Records
- Engineering Change Documents
- Design Failure Modes, Effects and Analyses (D-FMEA)
- Process Flow Diagram
- Process Failure Modes, Effects and Analyses (P-FMEA)
- Control Plan
- Measurement Systems Analysis (MSA / Gage R&R)
- Dimensional Results (for N parts)
- Raw Material Records
- Lab Results
- Functional Test Records
- Initial Sample Inspection Report
- Process Capability Study
- Appearance Approval Report
- Part Specification Warrant (PSW)
In addition, customers may provide requirements specific to their business and industry.
05. The Control Plan
A control plan defines all the product and process parameters that need to be controlled and verfied to ensure that the product meets requirements.
A typical control plan contains
- The parameter number (or balloon number)
- The parameter name (e.g. Diameter, Opacity, Position etc.)
- The Specification (e.g. 1.500 +/- .005)
- Unit of Measure (e.g. inch, ppm, fringes etc.)
- The number of times the feature reqpeats on the part (e.g. 3x)
- Inspection Method (CMM, Caliper, Micrometer)
- Work Instructions or Notes
- Key or Critical identifier
- Sampling Rules: Frequency (e.g. inspect 1 in 10) or Sample Size (AQL 1.0)
- Data Type: Numeric [Variable Data] e.g. 1.457, or Pass / Fail [Attribute Data]
- Operation Number and Description
- When the paprameter is inspected (Setup, In Process, Final, etc.)
- The reaction plan when something goes wrong
06. The PFMEA
A PFMEA is a list of all possible failure modes of a manufacturing process, the likelihood of ocurrence, along with the ability to prevent or detect, and severity when it does happen.
07. The Raw Material Record
The buyer will provide a raw material specification (e.g. AL6061 T6, 301SST etc.) and a reference standard. The supplier, in turn, must provide proof that the raw material used for the first article meets this specification.
This proof is provided in terms of a certificate of conformance (CoC) provided by the mill along with traceability information such as a Heat Lot number. The CoC will typically contain:
- The Mill Name
- Material Grade
- ASTM Standard Number
- Material Form and Dimensions
- Heat Lot Number
- Quantity Covered by the Report
- Actual Chemical Composition
- Mechanical Test Results
- Country of Origin
08. The Dimensional Record
The dimensional record will include Attribute Specifications (i.e. Pass/Fail or Yes/No) such as Part Engraving Checks, and Variable Specifications (i.e. Numeric or Measured Value) such as linear dimensions, diameters, positions etc. Data will be captured by a wide variety of measurement equipment including pin gages, calipers, micrometers, in-circuit testers, CMMs etc.
It is essential that each measurement be traceable to the gage that was used, and to the calibration record of the gage. And, an underlying assumption is that the gage has adequate resolution (typically 1/10th of the tolerance of the feature being measured), and that each measurement is repeatable and reproducible.
Note: The dimensional record by itself (without the raw material record and the special processing and functional testing records) may be meaningless. If you focus solely on the dimensional record, you run the risk of product functional failure.